Protective circuit and device for metal-oxide-semiconductor field effect transistor and method for fabricating the device

Abstract

A protective circuit comprises a metal-oxide-semiconductor field effect transistor (MOSFET) to be protected, and a depletion-type MOSFET the gate and source of which are connected to each other and the souce of which is connected to the gate of the MOSFET to be protected, whereby the protective circuit which is suitable for a high-speed operation is completed.

What is claimed is: 
     
       1. A protective circuit for a metal-oxide-semiconductor field effect transistor comprising: an input terminal to which input signals are applied; and   a depletion-type metal-oxide-semiconductor field effect transistor the gate and source of which are connected to each other, the source of which is connected to the gate of the transistor to be protected, and the drain of which is coupled to said input terminal.   
     
     
       2. A protective circuit according to claim 1, which further comprises an enhancement-type metal-oxide-semiconductor field effect transistor the gate and source of which are connected to each other and the drain of which is connected to the source of said depletion-type transistor. 
     
     
       3. A protective circuit according to claim 1, which further comprises a resistor connected between the drain of said depletion-type transistor and said input terminal. 
     
     
       4. A protective circuit according to claim 1, wherein the resistance between the drain and source is increased during increased voltage applied to said input terminal, such that increased potential of the source is suppressed.